Fiberline systems, processes and methods

ABSTRACT

A chemical pulp mill system and method of using black liquor flashing steam from a digester system comprises generating black liquor in the digester system, sending the black liquor to an evaporator system without using any pre-evaporator system, flashing the black liquor in the evaporator system to yield steam, and using at least some of the steam for chip steaming in a chip bin and/or for supplying in-direct heat exchangers in the digester system for pre-heating white liquor and/or filtrates for use in the digester system. In other embodiments, a chemical pulp mill system and method for utilizing black liquor flashing steam from a digester system comprises generating black liquor from the digester system, flashing the black liquor in one stage to yield steam prior to leading the black liquor into an evaporation system storage tank, using the steam to steam chips and/or evaporate black liquor in the evaporation system, and preventing formation of concentrated non-condensable gases and foul condensate in the digester system by using the digester system without any condenser for the black liquor flashing steam.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon U.S. Provisional Patent Application No.60/729,239, filed on Oct. 24, 2005, the entire disclosure of which isincorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

In conventional facilities producing chemical pulp utilizing continuousdigesters, the manner of handling the extracted black liquor from thedigester is to pass the black liquor to a pre-evaporation systemcomprising two flash tanks and a series of exchangers and then to passthe resulting liquor to other equipment in an evaporation/recoveryphase. See, e.g., FIG. 1.

According to the present invention, one embodiment of a continuouscooking and recovery system, process and method utilizes one or morestreams of black liquor extracted from the cooking system (i.e., thecooking system, which is also known as the digester system or digesterplant, includes the chip bin through the digester—and optionallyincluding an impregnation vessel) in an evaporation/recovery systemafter any pre-heater (if applicable) and without any pre-evaporationsystem (i.e., pre-evaporation equipment being equipment such as flashtanks, reboilers and exchangers where steam is generated as the blackliquor is cooled prior to sending the black liquor to the evaporationsystem in the recovery area).

According to another embodiment of the invention, black liquor from thedigester is sent to a flash tank and then to the evaporation/recoverysystem without using any flashing steam condenser.

The embodiments of the invention result in the improvement of the steameconomy of the fiberline system, improved recovery of the variousingredients used in the system, reduction of foul condensate andmalodorous gases, and/or reduced equipment and system requirements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a conventional fiberline system.

FIG. 2 is a schematic view illustrating a pre-evaporation andevaporation portion of a conventional fiberline system.

FIG. 3 is a schematic view illustrating an evaporation portion of afiberline system according to an embodiment the present invention.

FIG. 4 is a schematic view illustrating an evaporation portion of afiberline system according to an embodiment the present invention.

FIG. 5 is a schematic view illustrating a portion of a conventionalfiberline system.

FIG. 6 is a schematic view like that of FIG. 5, but illustrating anembodiment the present invention.

FIG. 7 is a schematic view like that of FIG. 5, but illustrating anotherembodiment the present invention.

DETAILED DESCRIPTION OF THE INVENTIVE EMBODIMENTS AND DRAWINGS

To assist in an understanding of the technology in the field and area ofthe invention, attention is directed to the attached documents, whichare incorporated herein by reference: U.S. Pat. Nos. 6,346,166,6,176,971, 6,132,555, 4,789,428 and 4,897,157, patent document nos.WO96/32531 and WO96/12848, and pages 183-184 of the book entitledPresent and Future Developments of Continuous Cooking and its FIG. 12.2.FIG. 12.2 (simplified as FIG. 1 herein) is an example of the currentstate of the art with regard to pre-evaporation and evaporation systems,including the following technology terms:

Pre-evaporation—in FIG. 1, see the dash-line box around flash tanks 10and 20 and the series of exchangers near the top of the figure andidentified as “PRE-EVAP.”

Pre-heaters—in FIG. 1, see the exchangers identified as “Pre-Heaters” inthe extraction line from the digester whose purpose is to use some ofthe heat in the extracted black liquor to “pre-heat” white liquor, otherblack liquor streams or other liquid streams being sent to the digesteror feed system.

Evaporator System—in FIG. 1, see the circled section identified as“EVAP.” In this area, there are a series of exchangers that are referredto as effects. Each effect produces steam from the black liquor thatenters the effect. The effects are numbered I through N, with Ioperating at the highest temperature and N operating at the lowesttemperature.

The current state of the art utilizes a fiberline system with a chip bin100 where steaming of wood chips or other cellulose material may or maynot be occurring, liquid is added to form a slurry, followed bypressurization of the slurry (this section is also referred to as thefeed system), fed to a treatment vessel or vessels (could be animpregnation vessel, a pre-hydrolysis process or other vessels),followed by a digester 5 (this section is also referred to as thecooking system). Currently, at least one black liquor stream (typicallyat a temperature of 110-150° C.) is withdrawn from the cooking system.The extracted black liquor stream or streams are used as a source ofheat to “pre-heat” white liquor, other black liquor streams, and/orother liquid streams being sent to the feed and cooking systems. Theextracted black liquor stream (or streams) is then sent to thepre-evaporation system, e.g., two or more flash tanks 10, 20 and/orreboilers where steam is produced from the hot black liquor as theliquor is cooled, typically to temperatures of about 95-110° C. At thispoint, the black liquor is sent to the evaporator system “EVAP” in therecovery area.

Once in the recovery area (FIG. 2), the “cool” black liquor entering therecovery area is stored in a “weak black liquor”(WBL) tank 30 until fedto the evaporator system. The evaporator system consists of a series ofeffects (numbered I to VI in FIG. 2) each operating at differenttemperatures and/or conditions to allow for the production of steamwhile cooling and concentrating the WBL. The concentration of the blackliquor leaving effect I, i.e., the highest temperature effect, is about75% solids, and is sent to a recovery boiler (not shown) to be burnedwhile the liquid stream out of the last effect VI is condensate at thelowest temperature (65° C. in FIG. 2) of the various effects and is usedthroughout the mill.

The WBL is introduced into the evaporator system at the effect which ismost appropriate (e.g., effect IV in FIG. 2), that means the effectwhere the temperature of the WBL will allow flashing to produce steam,typically the third or fourth effect. From this point of entry, theblack liquor flow is split, going in either direction (some black liquorgoes to hotter effects, which allows for the evaporation of the liquidand concentration of solids, other black liquor goes to lowertemperature effects and is heated and then sent to higher temperatureeffects for concentration). The solids content in the black liquor fromthe first effect is set (solids content such as 75% in FIG. 2).

One of the embodiments of the subject invention eliminates thepre-evaporator system. See FIGS. 3 and 4. In this inventive process, thetemperature of the WBL when sent to the recovery area is higher, therebyallowing for the WBL introduction into the evaporator system at aneffect that will allow for a greater production of steam.

It has also been discovered that the steam produced in this inventiveevaporator system is cleaner than that produced in a pre-evaporatorsystem at the digester area. The cleaner steam is suitable for use assteam for the chip bin 100 and can be drawn off the evaporator systembetween effects so that the steam going to the chip bin 100 has atemperature suitable for this use and thereby eliminates a steamingvessel, thus allowing for more efficient use of the steam produced inthe mill.

An advantage of this inventive process is the reduction of contaminatesintroduced into the chip bin in the steam, which, in turn, reducescontaminates in the gas vented out of the chip bin. The cleaner steamproduced in the evaporation system and used in the chip bin 100 reducesadverse emissions from the mill.

This inventive process also allows for the elimination of the WBLstorage tank external to the train of the evaporator system. The WBLstorage tank can become part of the evaporator system train, notexternal to the training, thereby saving costs.

The exemplary evaporator system shown in FIGS. 3 and 4 has otherimprovements over the conventional systems of FIGS. 1 and 2. The blackliquor stream coming from the digester 5 to the evaporator system ishigher in temperature. This stream can be sent directly to theappropriate effect in the evaporation system to improve the steamefficiency of the mill.

Optionally, a pressurized fiber filter 40 can be located in the linebetween the digester and the evaporator system to allow the removal offiber from the black liquor stream to a level of about 40 ppm leavingthe filter. The fiber material removed from the filter would be in theform of a slurry to be returned to the digester 5 or feed system.

In current systems that may arguably have a filter somewhat like this,the temperature of the stream entering the filter is too low (95-130°C.); thus, this stream material must be returned to the feed system tobe reheated to cooking temperature prior to further treatment. However,in the inventive process, the higher temperature of the black liquorstream from the digester to the evaporator system means the filteredmaterial is at a higher temperature. This higher temperature material iscloser to the cooking temperature and therefore can be returned to thetop of the digester, reducing the overall need for heat addition.Depending on the temperature of the material, a small portion of thestream from the digester could be sent through a cooler 50 and to asmaller tank 30 and to the evaporator system at the appropriate effect.

The inventive system has never been contemplated or used before becauseit has never been considered to “connect” the digester/cooking area andthe recovery area because of the distance between the two areas in themill and other factors. Another reason is the reliability of theseparation of each area. It is undesirable to have one of these areas“upset” that would cause a shutdown in the other area. Particularlydetrimental are upsets at the recovery area that would cause thedigester to be shut down. In short, loosing one area could cause extremeproblems in the other area. The inventive process overcomes theseproblems.

In another embodiment of the invention, a chemical pulping system,method and process utilizes a flashing tank. The prior art is firstdescribed, followed by the inventive embodiments.

In chemical pulping, cooking liquor at a high temperature is dischargedfrom a continuous digester. Typically, the discharged amount is 8-12m³/ADMT and the temperature on average is about 130-170° C. The cookingliquor discharged from the digester, i.e., black liquor, flows to anevaporation plant (containing pre-evaporation and evaporation systems),where, among other things, almost all the water present in the blackliquor is removed in several evaporation effects connected in seriesprior to black liquor combustion. Various black liquor evaporationeffects use fresh steam and flashing steam obtained from effects havinga higher temperature and pressure. In the evaporation plant, the blackliquor is led into a non-pressurized storage tank prior to the actualevaporation. Prior to the storage tank, the temperature of the blackliquor is decreased below 100° C. for preventing boiling in the tank.Between the digester and the storage tank of the evaporation plant, avery large amount of heat—1-4 GJ/ADMT—is removed from the black liquor.

Typically, several flashing tanks are used for removing heat from theblack liquor, wherein part of the hot black liquor converts intoflashing steam. If it was possible to remove by flashing the totalamount of heat mentioned above, the amount of water flashing, i.e.,vaporizing, would be 0.5-1.7 m³/ADMT. In practice, the temperature ofthe black liquor in the flashing tank decreases at best to a level ofabout 110° C., whereby the amount of water being vaporized is between0.3-1.3 m³/ADMT. Final cooling below 100° C. is typically performedindirectly in a heat exchanger, simultaneously providing hot water forpulp washing.

The amount of heat transferred into the flashing steam is typicallyutilized in chip steaming. In the chip steaming, the chips are heatedand the air contained therein is removed by means of steam, wherebysignificant advantages are achieved for the digesting process.Typically, steam is consumed during chip steaming, depending on the chipproperties and the steaming method, in the amount of about 0.5-2GJ/ADMT. As the above calculations indicate, the situation often is suchthat flashing steam is available in excess of steaming purposes.

Typically, this excess flashing steam is led to a separate flashingsteam condenser, where water vapor is condensed and simultaneously hotwater is obtained. The flashing steam contains compounds referred to asnon-condensable gases (methanol, turpentine, various sulfur compoundsetc.), which are removed from the condenser in gaseous form and at highconcentration. These gases are called concentrated malodorous gases. Achemical pulp mill also produces so-called weak malodorous gases,wherein the content of malodorous compounds is maintained underexplosive concentration. Condensed flashing steam contains othercompounds in addition to water, and it is called foul condensate. Thenon-condensable gases generated in the flashing steam condenser and thefoul condensate are led into other plants of the mill for furthertreatment, because if released into the atmosphere they would cause asignificant emission problem. As the concentrated malodorous gases andfoul condensate are toxic and explosive, the treatment thereof isdangerous and requires particular care.

It often happens, e.g., due to low capacity of the flashing steamcondenser, that the black liquor is not flashed to the maximum level ofabout 110° C., but the black liquor exits the flashing tank at a highertemperature. In that case, the flashing steam removal from the blackliquor is below maximum and the need for evaporation in the evaporationplant increases. In view of the overall energy efficiency of the mill,it is advantageous to remove as much flashing steam from the blackliquor as possible, provided that sensible objects of use are found,where it can be used to replace fresh steam with high efficiency.

Various techniques have been used for chip steaming. Conventionally, inaddition to atmospheric steaming, a short-term pressurized steaming hasbeen performed in a so-called steaming vessel or chip chute. Pressurizedsteaming is usually performed at a pressure of 1.0-1.5 bar. Pressurizedsteaming consumes a great amount of steam. Therefore, in connection withpressurized steaming, also the black liquor steaming is performed in twostages so that from the first stage the flashing steam is led into asteaming vessel and from the second stage into an atmospheric chip binwith a remarkably longer steaming retention time. In modern pulp mills,steaming in the chip bin is so efficient that pressurized steaming hasbeen omitted and typically only one black liquor flashing phase is used.This way, the process is simpler and the investment costs are lower.

FIG. 5 illustrates a typical system for utilizing the heat of blackliquor exiting the digester in a modern pulp mill. Black liquor from thedigester enters the flashing tank 1 via pipe 4. From the digesters,black liquor may be discharged to pipe 4 from more than one zone. As thepressure decreases, flashing steam is separated from the black liquor,which steam is led via pipe 5 into an atmospheric steaming phase and,depending on the situation, via pipe 6 to the flashing steam condenser2. More than one condenser may be used for condensing the flashingsteam. The flashing steam condenser receives cold (about 0-30° C.) orwarm (about 40-60° C.) water via pipe 11. As the steam condenses, thetemperature of this water increases and it discharges as hot water(about 65-90° C. ) via pipe 12 into the hot water system of the mill.Condensed steam exits as foul condensate via pipe 10 typically into thefoul condensate system of the digester plant and therefrom further to afoul condensate container of the evaporation plant. The non-condensablegases, i.e. concentrated malodorous gases, exit via pipe 9 into theconcentrated gases collection and treatment system. The black liquorflashed and cooled in the flashing tank exits via pipe 7 to black liquorcooler 3. There the temperature of the black liquor decreases furtherand it is discharged to the black liquor storage tank of the evaporationplant via pipe 8. The water used for black liquor cooling enters thecooler via pipe 13 and exits into the hot water system via pipe 14.

In modern fiberlines, the amount of hot water used in pulp washing hassignificantly decreased and often there is no reasonable use for thewhole amount of hot water generated in the flashing steam condenser andthe black liquor cooler, but the hot water has to be recooled andremoved from the plant. Thus, part of the heat amount of the blackliquor is lost. The objective of this embodiment of the invention is toutilize the excess flashing steam in a simple way, and simultaneouslyprevent the generation of concentrated malodorous gases and foulcondensates in the digesting plant.

The solution according to this embodiment of the invention does not usea flashing steam condenser, but the excess flashing steam is leddirectly to a suitable evaporation stage of the evaporation plant, whereit partly replaces fresh steam and thus improves the steam economy ofthe evaporation plant. Simultaneously, generation of foul condensate andconcentrated malodorous gases in the area of the digester plant isprevented and the treatment thereof can to that extent be restricted tothe evaporation plant, where they are inevitably treated anyway. Aprocess devoid of a flashing steam condenser and treatment ofconcentrated malodorous gases and foul condensate is naturally smallerthan a conventional process, including a favorable decrease ininvestment costs.

FIG. 6 illustrates a solution according to this embodiment of theinvention for flashing black liquor and utilizing flashing steam. Blackliquor from the digester enters the flashing tank 1 via pipe 4. From thedigester (or digesters), black liquor may be discharged to pipe 4 frommore than one zone. As the pressure decreases in the flashing tank 1,flashing steam is separated from the black liquor and led via pipe 5 toa steaming phase operating at atmospheric pressure and via pipe 15 tothe evaporation plant into a suitable condenser or other preferablelocation. No flashing steam condenser is used. As a result, thegeneration of foul condensate and concentrated malodorous gases in thedigester plant may be prevented. The black liquor flashed and cooled inthe flashing tank exits via pipe 7 to black liquor cooler 3. In thecooler 3, the temperature of the black liquor decreases further and itis discharged to the evaporation plant via pipe 8 (for example, into ablack liquor storage tank). The water used for black liquor coolingenters the cooler via pipe 13 and exits into the hot water system viapipe 14.

FIG. 7 illustrates another embodiment where the flashing steam is led tochip steaming only, and there is no flashing steam condenser. In thisembodiment, the black liquor from the digester enters the flashing tank1 via pipe 4. From the digester(s), black liquor may be removed frommore than one zone. As the pressure decreases in the flashing tank 1,flashing steam is separated from the black liquor, and flashing steam isled via pipe 5 only into an atmospheric steaming phase. Because noflashing steam condenser is used, generation of foul condensate andconcentrated malodorous gases in the digesting plant may be prevented.The black liquor flashed and cooled in the flashing tank exits via pipe7 to a black liquor cooler 3. There, the temperature of the black liquordecreases further and it is discharged to the evaporation plant via pipe8 (e.g., into a black liquor storage tank). The water used for coolingblack liquor enters the cooler via pipe 13 and exits into a hot watersystem via pipe 14.

Although this embodiment is a novel and good solution and preventsgeneration of concentrated malodorous gases and foul condensate in thedigester plant, it may have some drawbacks that can be addressed asfollows. If flashing steam is available in greater amounts than neededfor steaming, there is no way of utilizing this excess steam. Anotherdisadvantage becomes obvious during shutdowns of the plant, whereby theflashing steam may not be led to steaming and no flashing of blackliquor takes place. For this reason, the constructional pressure of theflashing tank should be significantly higher than normal in order toresist the high pressure resulting from the high temperature. Further,the cooling capacity of the black liquor cooler has to be much higherthan normal, so that the black liquor may be cooled under 100° C. evenin this situation. There is a further risk that in a situation where theflashing steam is not discharged from the flashing tank, concentratedmalodorous gases are enriched in the flashing tank. When flashing steamis taken into use again, a large amount of concentrated malodorous gasesmay erupt. This forceful and sudden eruption of concentrated malodorousgases may cause dangerous situations in the steaming area or devicesconnected thereto. In this embodiment according to the invention, noenrichment would take place because flashing steam is continuouslydischarged to the evaporation plant.

The use of flashing steam in evaporation has also been practiced inconnection with various pre-evaporation solutions. In these solutions,black liquor is flashed in several stages and flashing steam from apreceding stage is used for flashing of black liquor in the followingstage. The flashing steam used in chip steaming is typically obtainedfrom some pre-evaporator, and not directly from the flashing tank. Inaddition to the pre-evaporation plant, the mill also has a normalevaporation plant, where the dry solids content of the black liquor isincreased to a level high enough for combustion. In practice, thepre-evaporation plant solutions have often been complicated processesand prone to black liquor foaming. For these reasons, pre-evaporationplants are undesireable.

When using the inventive systems, processes and methods of theinvention, some may argue that the operation of the digester plant andthe evaporation plant are more dependent on each other than normal. Forexample, if the amount of flashing steam led into the evaporation plantvaries significantly, it may result in an irregular operation of theevaporation plant. This problem may be easily solved by stabilizing thesteam flow going to the evaporation plant by means of an optional flowcontroller 16 and allowing the amount of steam for steaming to change invarious fault situations of the digester plant. The amount of steamrequired for steaming may easily be compensated for in various faultsituations by means of fresh steam without any practical negative effecton the overall steam economy.

Another challenging situation might occur if the evaporation plant isnot in operation while the digester plant is operating. This situationis very rare and short-term because the black liquor storage tankbetween the digester plant and the evaporation plant fills quickly andwould not permit the digester plant to operate without the operation ofthe evaporation plant. In this situation, the previously presentedsolution may be utilized, where flashing steam is used for chip steamingonly. However, the sizing of the flashing tank and the black liquorcooler should be engineered for a situation where no flashing steam isremoved from the black liquor. Another solution is to lead the excessflashing steam to a condenser in the evaporation plant. Possiblecondensers include, e.g., a surface condenser following the evaporationplant or a condenser for a stripper used in cleaning foul condensatesfrom the evaporation plant. During short-term disturbances in theevaporation plant, these condensers can preferably receive steam. Incase of a longer-term shutdown of the evaporation plant, there is noreason to operate the digester plant.

In principle, the flashing steam from the flashing tank 1 may led intoany of the evaporation stages in the evaporation plant, where thepressure is low enough. Because the typical operational pressure in theflashing tank is about 0.2-0.5 bar overpressure, the evaporation stagesoperating at atmospheric or lower pressure are suitable. The mostpreferable solution, however, is to lead the steam into an evaporationunit having the highest possible pressure, because that provides thelargest possible saving of fresh steam. In a typical modern 7-stageevaporation plant, it would be most advantageous to lead the flashingsteam to the third evaporator stage. In that case, the flashing steamwould be present and working in five evaporation stages and allow forsaving fresh steam in a proportion of 5:7. In other words, one kilogramof flashing steam would decrease the consumption of fresh steam by 5/7kilos. The use of flashing steam in the evaporation plant is mostadvantageous when the evaporation plant has at least six evaporationstages.

The principles of the invention may also be applied in situations wherethere is more than one flashing tank and also a pressurized steamingphase is used. When several flashing tanks are used, higher-pressurefractions may be separated from the total amount of flashing steamavailable, and the higher-pressure fractions may be used for variouspurposes. Nevertheless, the use of several flashing stages gives only amarginal benefit compared to the simple solution based on a singleflashing stage according to the invention because, with the solutionutilizing one flashing tank, all the flashing steam generated can beefficiently utilized in steaming and in the evaporation plant.“Efficient use” of flashing steam means that it replaces fresh steamusage with high efficiency. For this reason, the solution according tothe invention is most advantageous when using one flashing tank.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements and variations included withinthe spirit and scope of the appended claims.

1. A method of using black liquor flashing steam from a digester systemof a chemical pulp mill, said method comprising: (a) generating blackliquor in the digester system, (b) sending the black liquor to anevaporator system without using any pre-evaporator system, (b) flashingthe black liquor in the evaporator system to yield steam, and wherein atleast some of the steam is used for chip steaming in a chip bin and/orfor supplying in-direct heat exchangers in the digester system forpre-heating white liquor and/or filtrates for use in the digestersystem.
 2. A method according to claim 1 wherein the temperature of theblack liquor sent to the evaporator system is about 110° C. to about150° C.
 3. A method according to claim 1 wherein the temperature of theblack liquor sent to the evaporator system is about 130° C. or greater.4. A method according to claim 1 wherein the temperature of the blackliquor sent to an effect in the evaporator system is about 110° C. toabout 150° C.
 5. A method according to claim 1 wherein the temperatureof the black liquor sent to an effect in the evaporator system is about130° C. or greater.
 6. A method according to claim 1 further utilizing apressurized fiber filter between the digester system and the evaporatorsystem.
 7. A method according to claim 6 wherein the filter allows theremoval of fiber from the black liquor stream to a level of about 40 ppmleaving the filter.
 8. A method according to claim 1 wherein theevaporator system includes a multi-effect evaporator having at least sixeffects.
 9. A chemical pulp mill system comprising: (a) a digestersystem that can generate black liquor, (b) an evaporator system, whereinthe chemical pulp mill system has no pre-evaporator system, and whereinblack liquor can be flashed in the evaporator system to yield steam, andat least some of the steam can be used for chip steaming in a chip binand/or for supplying in-direct heat exchangers in the digester systemfor pre-heating white liquor and/or filtrates for use in the digestersystem.
 10. A system according to claim 9 further comprising apressurized fiber filter between the digester system and the evaporatorsystem.
 11. A system according to claim 10 wherein the filter can allowthe removal of fiber from a black liquor stream to a level of about 40ppm leaving the filter.
 12. A system according to claim 9 wherein theevaporator system comprises a multi-effect evaporator having at leastsix effects.
 14. A system according to claim 9 comprising two or moredigesters.
 15. A method for utilizing black liquor flashing steam from adigester system of a chemical pulp mill, said method comprising: (a)generating black liquor from the digester system, (b) flashing the blackliquor in one stage to yield steam prior to leading the black liquorinto an evaporation system storage tank, (c) using the steam to steamchips and/or evaporate black liquor in the evaporation system, and (d)preventing formation of concentrated non-condensable gases and foulcondensate in the digester system by using the digester system withoutany condenser for the black liquor flashing steam.
 16. A methodaccording to claim 15 wherein the steam is used to simultaneously steamchips and evaporate black liquor in the evaporation system.
 17. A methodaccording to claim 15 further comprising cooling the black liquor in ablack liquor cooler after flashing.
 18. A method according to claim 15further comprising stabilizing the steam flow going to the evaporatorsystem with a flow controller.
 19. A method according to claim 15wherein the evaporator system includes a multi-effect evaporator havingat least six effects.
 20. A chemical pulp mill system comprising: (a) adigester system that can generate black liquor, (b) a flash tank forflashing the black liquor to yield steam, and wherein the system doesnot have any condenser for the black liquor flashing steam yet thesystem is capable of preventing the formation of concentratednon-condensable gases and foul condensate in the digester system.
 21. Asystem according to claim 20 that further comprises an evaporator systemhaving a multi-effect evaporator with at least six effects.
 22. A systemaccording to claim 20 that further comprises a black liquor cooler afterthe flash tank.
 23. A system according to claim 20 that furthercomprises at least one flow controller after the flash tank.
 24. Asystem according to claim 22 that further comprises a flow controllerafter the cooler.